Sorry that it crashed, and doubly sorry that it crashed mid-game! Mirklings was my first web port and I'm still trying to figure things out.
My best guess is that the game ran out of memory. Since emscripten is not that hot at handling dynamic memory alloc, I decided to go with the name-an-upper-memory-limit-at-compile-time strategy. I'll reupload it with a larger memory pool. Once again, really sorry!